The invention relates to a non-return valve in which a hollow, conoidally-shaped diaphragm of elastomerically deformable material is seated in a perforate, hollow, conoidally-shaped valve seat.
In a non-return valve such as this, the diaphragm is inwardly deformable when the pressure differential across the valve reaches a predetermined value, so as to allow fluid to pass through the valve seat. When the pressure differential falls below this predetermined value, the diaphragm resumes its underformed shape so as to seal against the valve seat and thereby prevent return flow.
In practice, the rim of such a diaphragm does not deform uniformly around its periphery, it deforms so that at least one portion of the outer surface of the diaphragm extending from the rim forms an outwardly concave surface. This irregular deformation of the valve member can result in a slow response to a reversal of pressure gradient and so various attempts have been made in order to ensure that the valve member will deform in a regular and predictable manner.